M. M. Ayoub

Problems and solutions in manual materials handling: the state of the art

For several decades manual materials handling has been a topic of interest in many fields of research. The reason for this interest is the devastating cost of and human suffering caused by injuries associated with MMH. Prevention and control of these injuries has been a concern shared by many researchers. In order to control the nature and extent of these injuries, limits must be established for MMH, especially lifting. This paper summarizes the variables affecting the ability to handle materials and the three basic approaches to determining capacities and limits for MMH: the biomechanical, the physiological, and the psychophysical approaches. The paper presents the various models developed in each of these approaches, together with a discussion of progress made and difficulties encountered in deriving capacity recommendations from each. Finally, the paper presents the latest recommendation on how these approaches can be integrated into a single comprehensive model for establishing lifting limits.

The influence of gender, grasp type, pinch width and wrist position on sustained pinch strength

Abstract Sustained pinch strength data were collected from eight male and eight female subjects using a modified Caldwell regimen for pinch strength. Four independent variables were investigated: gender, wrist position, grasp type, and pinch width. All main effects were significant at the α = 0.05 level, and several 2-way interactions were significant. The effects of wrist position and grasp type were fairly well predicted by previous research; however, no published research has investigated the effects of pinch width. Based on the results of this study, it appears that the optimal pinch width is close to 5 cm, and this value may be different for males and females. The data reported here are considerably lower than other published data, probably because previous research has concentrated on peak strength, suggesting that peak pinch strength data should be used with caution as they may overestimate pinch strength capabilities.

Development of Strength and Capacity Norms for Manual Materials Handling Activities: The State of the Art

Literature related to manual materials handling activities is reviewed and recommendations are made for the maximum acceptable weight of lift for male and female workers, based on the psychophysical approach.

Development of methodology in biomechanical simulation of manual lifting

Abstract The purpose of this paper is to introduce some techniques of biomechanical simulation through an example — simulation of manual lifting. The motivation for developing biomechanical simulation is discussed. Biomechanical simulation is defined and compared with the traditional biomechanical modeling. The formulation of biomechanical simulation of manual lifting is presented, and some practical techniques used to conduct a simulation of manual lifting are provided.

Review, Evaluation, and Comparison of Models for Predicting Lifting Capacity

Models related to lifting activities have been classified and reviewed. Predictive models are grouped under psychophysical capacity modeling, physiological energy requirement modeling, and biomechanical stress modeling. Within each group, the models have been compared and evaluated. In addition, psychophysical and physiological model groups have been compared.

Fuzzy modelling of stresses in manual lifting tasks.

Abstract A new approach, based on the theory of fuzzy sets and systems, was proposed to assess the acceptability of stresses involved in manual lifting tasks. Nine male subjects participated in a laboratory lifting experiment. A total of 108 data points (9 subjects × 4 levels of frequency × 3 replications) were collected. The maximum acceptable weights of lift were determined using the psychophysical methodology. Metabolic energy expenditure and heart rates were also measured. A hypothesis, stating that the combined effect of biomechanical and physiological stresses leads to an overall measure of lifting task acceptability as expressed by the psychophysical stress, was suggested and evaluated. Conditions were found for which the acceptability measures of the combined and the psychophysical stresses were close to one another. A concept of safety index for a particular weight of load lifted was also proposed.

An ergonomics approach for the design of manual materials-handling tasks.

The frequency, severity, and cost of manual materials-handling (MMH) injuries dictate that the design of these tasks and the assignment of employees to them ensure that the demands of the job do not exceed the capacity of the worker. This paper proposes the use of the job Severity Index (JSI) as a tool for job design and employee placement. The JSI is defined as the time- and frequency-weighted average of the maximum weight required by each task divided by the selected lifting capacity given the lifting task conditions. This paper illustrates the relationship between the JSI and the frequency, severity, and cost of MMH injuries. Procedures for job design and employee placement based on the JSI are discussed and examples of the use of the JSI in industry are given.

The psychophysical approach to manual materials handling task design

For approximately three decades, researchers have utilized psychophysics to develop guidelines (weights, forces and frequencies) for manual materials handling tasks. Early work by Stover Snook and his colleagues provided the foundations of the experimental methodologies that would be used by other researchers as well as design data that would be used by practitioners. Currently, there are extensive psychophysical data for designing a variety of materials handling tasks. The current state of psychophysical data will be examined, and the psychophysical approach will be compared to the biomechanical and physiological approaches to setting limits for materials handling tasks. The advantages and disadvantages of the psychophysical approach will be discussed, as will the research needs required to address the current limitations of the psychophysical approach.

Effects of an endurance and strength training programme on lifting capability of males

Abstract Back injuries resulting from manual materials handling are one of the major sources of compensation claims and time lost from work. One of the possible means of reducing human susceptibility to musculoskeletal injuries is by increasing the individuals lifting capability by prior training. This paper describes a 6 week training programme that successfully increased the maximal oxygen uptake, isometric strength and lifting capability of 10 male subjects. The programme trained subjects for flexibility, muscle strength (by applying the concept of progressive resistance exercise), muscle endurance (by lifting light loads at high frequency of lift) and cardiovascular endurance (by exercising on a bicycle ergometer). The training programme resulted in significant increase in the maximal oxygen uptake and isometric back, arm, leg and shoulder strengths of the subjects. The maximum acceptable weight lifted, using a compact box for different heights of lift, also increased significantly.

Work Place Design and Posture

The physical well-being, comfort, and, hence, the ability to perform a given task are influenced by the design of the work place. This paper presents a brief summary of some of the critical dimensions in work place design. The illustrations show the work space design for both the male and female worker. A guideline for working posture is included to assist in avoiding pitfalls in the design of the work and the work place.